This invention relates generally to multimodal ethylene, alpha-olefin and diene polymer compositions, processes for making them and to devices comprising such compositions. These compositions have been found to have an improved balance of processability, resilience and durability.
Elastomers useful in applications requiring high resilience have in general a high elasticity in the medium to high frequency range (typically between 5 and 600 rad/sec) which results in low loss tangent (tan xcex4), at temperatures ranging from approximately room temperature to over 100xc2x0 C. Natural rubber is an elastomer of this type.
Ethylene elastomers contain sufficient copolymerised alpha-olefin to produce amorphous to semi-crystalline compounds of density generally below 0.9. In the class of ethylene based elastomers, such as EPDM elastomers, polymers of very high molecular weight (as measured by their Mooney viscosity) are usually required for high resilience applications. Although high molecular weight EPDM elastomers are commercially available, their inherently very high viscosity (Mooney viscosity in general greater than 200) creates difficulties in processability which requires them to be produced with the addition of extender oil to reduce their apparent viscosity. Very high molecular weight polymers are not only difficult to separate from their polymerization solvent without inducing significant macromolecular chain breakage, but they are difficult to mix and compound. The addition of extender oil to the elastomer eases processability in terms of production process recovery, elastomer mixing and compounding.
The required level of extender oil depends on the molecular weight of the elastomer, but is usually sufficient to reduce the apparent viscosity to a Mooney viscosity of about 100 or below. Typical extender oil level is in general in the range of from 10 to 150 phr. Commercially available very high molecular weight EPDMs which would be useful in high resilience applications contain from about 50 to about 125 phr extender oil.
Problems arise from the use of extender oil however. Elastomers extended with oil are limited in compounding latitude since they already contain a level and/or type of oil which may be undesirable in the compound recipe and restrict further compounding options. Furthermore, the extender oil simply acts as a processing aid and does not participate in the formation of a tight cross-link network upon vulcanization, which reduces the elasticity of the vulcanized compounds.
The elasticity of ethylene based elastomers can be increased by introducing long chain branches into their structure. This can be achieved using certain acidic transition metal catalysts, or through the use of dienes having two polymerizable double bonds such as norbornadiene, dicyclopentadiene, vinyl norbornene or alpha-omega dienes. However, a high level of branching is required for significantly improved elasticity, and such branching can result in polymers that are almost impossible to process without the use of extender oil as described above. Moreover, the presence of long chain branching adversely affects physical properties such as tear resistance, tensile strength and elongation.
Another method of increasing processability is to produce bimodal elastomers having a major fraction of lower molecular weight polymer (Mooney viscosity less than about 100) and a minor fraction of high molecular weight polymer (Mooney viscosity greater than 120), as in ExxonMobil Chemical""s Vistalon(trademark) Bimodal EPDM grades. However, these polymers tend to have an elasticity which is too low.
Among the more demanding applications for processable, highly elastic applications are vibration damping devices. Vibration damping devices are used to absorb vibrational energy generated by machines such as automobile, jet and other engines, air conditioners, vehicle exhaust systems and other dynamic devices that generate significant vibration during operation. Unless a damping device is used, this vibration is directly transmitted to support and surrounding structures. The result can range from annoying to destructive. The damping device should maintain its performance under a wide range of temperature and other environmental conditions and for a relatively long period of time.
Examples of vibration damping devices include formed shapes, mountings, harnesses, rings, bushings and belts used to isolate vibrators from what would otherwise be vibrated. While natural rubber is often used in vibration damping applications because it provides high resiliency and desirable physical properties like tear resistance, natural rubber does not last long under conditions of extreme heat ( greater than 120xc2x0 C.) or ozone concentration such as is found in many automotive applications.
Despite years of research in this area there is still a need for economically produced synthetic materials that have an improved balance of processability, resilience and durability.
U.S. Pat. No. 3,884,993 describes the preparation of the blends via a parallel reactor process using traditional Ziegler-Natta catalysts. These blends have a maximum Mooney viscosity of 53 (1+8@121xc2x0 C.) which corresponds to a Mooney viscosity of about 57 when measured at 1+4@125xc2x0 C. even where the amount of high molecular weight fraction reaches approximately 58 weight percent. The low molecular weight fraction has an Mn below 25,000.
WO00/26296 discloses an ethylene-alpha olefin elastomeric composition made by a series reactor operation in which the high molecular weight component has a Mooney not exceeding 120 and is present in an amount no greater than 50 weight percent.
U.S. Pat. No. 4,078,131 describes blends of EPDM having components with differing average propylene contents. A wide range and variation of properties in the components is disclosed, but there is no disclosure of a blend comprising 50 weight percent or more of a high molecular weight fraction having a Mooney of over 120.
In the invention a multiple reactor process may be used to produce an elastomer of high Mooney viscosity in one reactor, while a second reactor in series or parallel produces an elastomer of low Mooney viscosity which acts as an internal plasticizer for the high Mooney viscosity polymer component thereby producing an elastomer having an overall Mooney viscosity low enough to enable easy processing while maintaining normal compounding operations. The composition is solid, that is to say not fluid at room temperature, and substantially free of solvent. The composition can be formed into bales or pellets for subsequent processing, compounding and mastication.
In a polymer product aspect of the invention there is provided a multimodal elastomer including a fraction of high Mooney viscosity and a fraction of low Mooney viscosity which acts as an internal plasticizer for the high Mooney viscosity polymer fraction thereby producing an elastomer having a Mooney viscosity low enough to enable easy processing while maintaining normal compounding operations. The elastomeric nature of the internal plasticizing component allows it to participate in a cross-linked network upon vulcanization. Some forms of the invention may provide a polymer providing high resiliency and durability even under exposure to prolonged high temperature conditions.
In an elastomer compound aspect of the invention there is provided a formulation containing a polymer of the invention; conventional fillers, cross-linking and stabilizing additives, plasticizing oil and optionally other compounding ingredients. Compared to recipes containing high Mooney viscosity polymers extended with oil, the total amount of plasticizing oil in the recipe can be reduced.
In one embodiment the invention is a solid multimodal polymer composition comprising units derived from ethylene, alpha-olefin and diene, said polymer composition having a tan (xcex4) of 0.5 or less when measured at 125xc2x0 C. and at a frequency of 10.4 rad/sec, and an overall Mooney viscosity of at least 60 (1+4@125xc2x0 C.); said polymer comprising: at least 50 weight percent based on the total polymer weight of a first fraction having a Mooney viscosity of over 120 (1+4@125xc2x0 C.); and from 5 to 50 weight percent based on the total polymer weight of a second fraction having a Mooney viscosity of 120 or less (1+4@125xc2x0 C.) and a Mn of at least 3500 g/mol.
In another embodiment the invention is a solid multimodal polymer composition comprising units derived from ethylene, alpha-olefin and diene, said polymer composition having a tan (xcex4) of 0.5 or less when measured at 125xc2x0 C. and at a frequency of 10.4 rad/sec, and an overall Mooney viscosity of at least 30 (1+4@125xc2x0 C.); said polymer comprising: a) at least 60 weight percent based on the total polymer weight of a first fraction having a Mooney viscosity of over 120 (1+4@125xc2x0 C.); and b) from 5 to 40 weight percent based on the total polymer weight of a second fraction having a Mooney viscosity of 120 or less (1+4@125xc2x0 C.) and a Mn of at least 3500 g/mol.
In another embodiment the invention is a solid multimodal polymer 30 composition comprising units derived from ethylene, alpha-olefin and diene, said polymer composition having a tan (xcex4) of 0.5 or less when measured at 125xc2x0 C. and at a frequency of 10.4 rad/sec, and an overall Mooney viscosity of at least 30 (1+4@125xc2x0 C.); said polymer comprising: a) at least 50 weight percent based on the total polymer weight of a first fraction having a Mooney viscosity of over 120 (1+4@125xc2x0 C.) and a molecular weight distribution of 3.0 or less; and b) from 5 to 50 weight percent based on the total polymer weight of a second fraction having a Mooney viscosity of 120 or less (1+4@125xc2x0 C.), a molecular weight distribution of 3 or less, and a Mn of at least 25000.
In still another embodiment the invention is a multimodal polymer composition comprising from 40 to 90 mole percent ethylene derived units, from 0.2 to 5.0 mole percent non-conjugated diene derived units, and the remainder of the polymer units comprised of propylene derived units; said polymer composition being essentially free of oil additive and having a tan (xcex4) less than 0.5 when measured at 125xc2x0 C. and at a frequency of 10.4 rad/sec, an overall Mooney viscosity of from 30 to 100(1+4@125xc2x0 C.), a branching index of at least 0.7, and said polymer comprising: a) at least 50 weight percent based on the total polymer weight of a first fraction having a Mooney viscosity of over 120 (1+4@125xc2x0 C.) and a molecular weight distribution of 3 or less; and b) from 5 to 50 weight percent based on the total polymer weight of a second fraction having a Mooney viscosity of 120 or less (1+4@125xc2x0 C.), a Mn of at least 3500 and a molecular weight distribution of 3 or less; and wherein the amount (wt %) of ethylene derived units in the first and second fraction differ by no more than 20%.
In still another embodiment the invention is a multimodal polymer composition comprising units derived from ethylene, alpha-olefin and diene, said polymer composition having a tan (xcex4) of 0.5 or less when measured at 125xc2x0 C. and at a frequency of 10.4 rad/sec, and an overall Mooney viscosity of at least 30(1+4@125xc2x0 C.); said polymer comprising: a) at least 50 weight percent based on the total polymer weight of a first fraction (also referred to herein as fraction a)) having a Mooney viscosity of over 120 (1+4@125xc2x0 C.); and b) from 5 to 50 weight percent based on the total polymer weight of a second fraction (also referred to herein as fraction b)) having a Mooney viscosity of 120 or less (1+4@125xc2x0 C.) and a Mn of at least 3500 g/mol. In a particular aspect of any of the embodiments described herein, the composition has one or more of the following characteristics, in any combination:
a. the composition is solid;
b. the composition has an overall Mooney viscosity of at least 60(1+4@125xc2x0 C.);
c. the composition has an overall Mooney viscosity of less than 100(1+4@125xc2x0 C.);
d. the composition has an overall Mooney viscosity of from 30 to 100 (1+4@125xc2x0 C.);
e. the composition comprises at least 60 weight percent based on the total polymer weight of a first fraction and from 5 to 40 weight percent based on the total polymer weight of a second fraction;
f. the composition comprises at least 70 weight percent based on the total polymer weight of a first fraction and from 5 to 30 weight percent based on the total polymer weight of a second fraction;
g. the first fraction has a Mooney viscosity of over 120 (1+4@125xc2x0 C.);
h. the first fraction has a Mooney viscosity of at least 175 (1+4@125xc2x0 C.);
i. the second fraction has a Mooney viscosity of 120 or less (1+4@125xc2x0 C.);
j. the second fraction has a Mooney viscosity below 50 (1+4@125xc2x0 C.);
k. the fraction a) and b) have a molecular weight distribution of 4 or less, preferably 3 or less;
l. the fraction b) has a Mn above 3500 g/mol;
m. the fraction b) has a Mn of at least 25000 g/mol;
n. the composition comprises from 35, preferably 40, to 90 mole percent ethylene derived units, from 0.2 to 5.0 mole percent non-conjugated diene derived units, and the remainder of the polymer units derived from propylene;
o. fraction a) comprises less than 78 wt %, preferably less than 72 wt % and especially less than 65 wt % of ethylene derived units based on the total weight of ethylene and alpha-olefin;
p. fractions a) and b) have a diene content less than 15 wt %, preferably less than 12 wt % and especially less than 10 wt % based on the total weight of ethylene, alpha-olefin, and diene;
q. the diene contents of fractions a) and b) differ by less than 8%, preferably less than 5 wt % and especially less than 3 wt %;
r. the polymer composition is essentially free of oil additive;
s. the polymer composition has a branching index of at least 0.7, preferably at least 0.8;
t. the amount (wt %) of ethylene derived units in fraction a) and b) differ by no more than 20%, preferably by no more than 10%;
u. the fraction b) has a Mv of at least 9000 g/mol;
v. the composition has a tan (xcex4) of 0.45 or less, and is preferably between 0.1 and 0.4, when measured at 125xc2x0 C. and at a frequency of 10.4 rad/sec; and
w. the polymer composition contains less than 30, preferably less than 20, and especially less than 10 parts by weight oil per 100 parts by weight polymer.
In another embodiment the invention is a process, preferably a series reactor process, for the preparation of multimodal polymer composition comprising: contacting in a first reactor activated metallocene catalyst with ethylene, diene and propylene monomers thereby producing an effluent containing a first polymer component; feeding the effluent to a second reactor wherein activated metallocene catalyst is contacted with additional ethylene, diene and propylene monomers to produce a second polymer component and final product; and controlling conditions in each reactor in order to obtain a first polymer component having a Mooney viscosity of over 120 (1+4@125xc2x0 C.) and a second polymer component having a Mooney viscosity of 120 or less (1+4@125xc2x0 C.) and a Mn of at least 3500 g/mol, and the final product has tan (xcex4) of 0.5 or less when measured at 125xc2x0 C. and at a frequency of 10.4 rad/sec, has an overall Mooney viscosity of at least 30 (1+4@125xc2x0 C.),and contains no more of the second polymer component than the first polymer component.
In another embodiment the invention is a vibration damping device comprising a multimodal polymer composition containing units derived from ethylene, alpha-olefin and diene, said polymer composition having a tan (xcex4) of 0.5 or less when measured at 125xc2x0 C. and at a frequency of 10.4 rad/sec, and an overall Mooney viscosity of at least 30 (1+4@125xc2x0 C.); said polymer comprising a) at least 50 weight percent based on the total polymer weight of a first fraction having a Mooney viscosity of over 120 (1+4@125xc2x0 C.); and b) from 5 to 50 weight percent based on the total polymer weight of a second fraction having a Mooney viscosity of 120 or less (1+4@125xc2x0 C.) and a Mn of at least 3500 g/mol.